Molecular and morphological systematics of the crinoid-parasitic snail genus Goodingia (Mollusca: Caenogastropoda: Eulimidae) with new insights into intrafamilial phylogenetic relationships

Abstract

Goodingia is a crinoid-parasitic genus of the gastropod family Eulimidae, consisting of two named members: G. varicosa (Schepman, 1909) (type species) and G. capillastericola (Minichev, 1970). Due to their rarity, these species have been scarcely compared with each other. In this study, we assessed the taxonomic and phylogenetic relationships of Goodingia plus an undescribed eulimid species, whose parasitic ecology and shell profile accord with the genus, with morphological and molecular data. Shell resemblance justified a close relationship between the two species of Goodingia. Newly collected specimens of G. capillastericola from Papua New Guinea and Japan were morphologically indistinguishable but were genetically differentiated from each other (uncorrected p distances of 8.1–8.8% in mitochondrial COI sequences). Phylogenetic analysis recovered another crinoid-parasitic genus Annulobalcis as a paraphyletic group to G. capillastericola, suggesting the evolutionary transition of shell shape from slender to globose and of sexual strategy from separate sexes to simultaneous hermaphroditic. Unexpectedly, the Goodingia-like undescribed species was phylogenetically distant from Goodingia and even Annulobalcis. The present eulimid phylogeny also suggested the polyphyly of endoparasitic and radula-less taxa, respectively, and multiple acquisition of the pseudopallium in the endoparasitic taxa.